System and inspection method

ABSTRACT

A system includes a first device with a primary screening area; a second device with a secondary screening area different from the primary screening area; and processor circuitry. The first device includes a first antenna and a first communication device; the second device includes a second antenna and a second communication device. The first antenna irradiates an electromagnetic wave to a target in the primary screening area and receives an electromagnetic wave reflected by the target; the second antenna irradiates an electromagnetic wave to the target in the secondary screening area and receives an electromagnetic wave reflected by the target; and the processor circuitry determines a possibility that the target possesses a predetermined article, based on a level of the electromagnetic wave received by the first antenna, and determines that screening by the second device is required for the target in accordance with the possibility. The first communication device transmits, to the second device, first information identifying that screening by the second device is required for the target; and the processor circuitry makes the second antenna start irradiation of the electromagnetic wave when the second communication device receives the first information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. application Ser.No. 16/807,354, filed on Mar. 3, 3030, which is based upon and claimsthe benefit of priority from Japanese Patent Application No.2019-112009, filed Jun. 17, 2019, the entire contents of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to a system and aninspection method.

BACKGROUND

Many inspection systems of determining whether a target person of aninspection has a dangerous article with being hidden have been proposed.As an example, an inspection apparatus irradiates an electromagneticwave to the target person, receives a reflection wave from the targetperson, and performs high-definition imaging of a dangerous articlebased on the amplitude of the received signal. In such an apparatus thatperforms high-definition imaging, it is necessary to irradiate anelectromagnetic wave to a very large number of points of the targetperson, and thus it takes a lot of time for inspection.

As a method of determining possession of a dangerous article in a shorttime, a following method is proposed. In this method, an electromagneticwave is irradiated to at least two points of the target person.Reflection waves from clothes and reflection waves from the body aredetected for each irradiation, and an optical distance between theclothes and the body is calculated based on a difference betweendetection signals. If there is a difference between optical distances ofat least two points, and the difference is equal to or greater than athreshold value, it is determined that the target person has adielectric explosive hidden between the clothing and the body.

However, since the distance between the clothes and the body is verysmall, a high resolution is required for calculating the opticaldistance. In general, the electromagnetic wave reflectance of clothes islow. In particular, wool clothing such as a sweater hardly reflects anelectromagnetic wave. For this reason, in an actual environment withmany interferences and much noise, the reflection wave from the clothesis buried in the noise and the interferences, and thus it is difficultto detect such a reflection wave. Therefore, it is difficult tocalculate the optical distance with high accuracy.

Further, since this method is based on the premise that the optical pathis extended by the presence of the dielectric, the dangerous articleallowed to be detected is limited to explosives, and it is not possibleto detect a metallic dangerous article such as a handgun.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams illustrating an outline of an example of adangerous-article screening system including a system according to anembodiment.

FIG. 2 is a block diagram illustrating an example of an electricalconfiguration of the system according to the embodiment, which functionsas a primary screening system.

FIG. 3 is a block diagram illustrating an example of an electricalconfiguration of a radar in the system according to the embodiment.

FIGS. 4A and 4B are diagrams illustrating a first example of scanning bythe radar.

FIGS. 5A and 5B are diagrams illustrating an example of a chirp signaltransmitted by the radar.

FIG. 6 is a diagram illustrating an example of Fast Fourier Transform(FFT) performed by the radar.

FIGS. 7A, 7B, and 7C are diagrams illustrating an example of dangerousarticle screening according to the embodiment.

FIG. 8 is a diagram illustrating an example of a determination result ofthe dangerous article screening according to the embodiment.

FIG. 9 is a flowchart illustrating an example of primary screening inthe system according to the embodiment.

FIGS. 10A and 10B are diagrams illustrating a second example of thescanning by the radar.

FIG. 11 is a diagram illustrating a third example of the scanning by theradar.

FIG. 12 is a diagram illustrating a fourth example of the scanning bythe radar.

FIG. 13 is a diagram illustrating a fifth example of the scanning by theradar.

FIGS. 14A and 14B are diagrams illustrating a sixth example of thescanning by the radar.

FIGS. 15A and 15B are diagrams illustrating a seventh example of thescanning by the radar.

FIGS. 16A, 16B, 16C, 16D, 16E, 16F, and 16G are diagrams illustratingother examples of the scanning by the radar.

FIG. 17 is a block diagram illustrating an example of an electricalconfiguration of the system according to the embodiment, which functionsas a secondary screening system.

FIG. 18 is a diagram illustrating an example of an array antenna shownin FIG. 17.

FIGS. 19A and 19B are diagrams illustrating an example of a first imageand a second image respectively obtained by a first sub-array antennaand a second sub-array antenna forming the array antenna shown in FIG.18.

FIG. 20 is a graph illustrating an example of profiles of the firstimage and the second image shown in FIGS. 19A and 19B.

FIG. 21 is a diagram illustrating an example of an image of a targetperson, which is obtained by the system shown in FIG. 17.

FIG. 22 is a flowchart illustrating an example of processing in thesystem shown in FIG. 17.

DETAILED DESCRIPTION

Hereinafter, an embodiment will be described with reference to thedrawings. The following descriptions are provided to exemplify anapparatus and a method for embodying the technical idea of theembodiment. The technical idea of the embodiment is not limited to astructure, shapes, arrangement, materials, and the like of componentsdescribed below. Modifications easily conceivable by those skilled inthe art are naturally included in the scope of the disclosure. In orderto make the descriptions clearer, in the drawings, each element may beschematically expressed by changing the size, the thickness, the planardimension, the shape, or the like of the element from that in an actualembodiment. In a plurality of drawings, elements having differentdimensional relations and different ratios may be included. In theplurality of drawings, corresponding elements may be denoted by the samereference signs, and repetitive descriptions may be omitted. Although aplurality of names may be given to some elements, the names are merelyexamples, and other names are given to the elements. Other names aregiven to elements to which a plurality of names are not given. In thefollowing descriptions, “a connection” means not only a directconnection, but also an indirect connection through another element.

In general, according to one embodiment, a system comprises a firstantenna and first processor circuitry. The first antenna is configuredto irradiate a first electromagnetic wave of a wavelength of 1 mm to 30mm to a first position in an area in which at least one of a targetperson or a belonging of the target person is present, and irradiate asecond electromagnetic wave of a wavelength of 1 mm to 30 mm to a secondposition in the area different from the first position in the area. Thefirst processor circuitry configured to obtain a first reflectionintensity of the first electromagnetic wave on the first position, andobtain a second reflection intensity of the second electromagnetic waveon the second position, and determine a degree of danger relating to apossibility that the target person possesses a dangerous article, basedon a difference between the first reflection intensity and the secondreflection intensity.

EMBODIMENT Screening System

A system according to the embodiment will be described. The systemaccording to the embodiment can be applied to various inspectionapparatuses. However, the embodiment relates to a dangerous-articlescreening system. The system detects a person who possesses a dangerousarticle such as a handgun or an explosive, in a facility in which anunspecified number of people gather, such as an airport, a station, ashopping mall, a concert hall, and an exhibition hall. Since the personmoves, the person may not stay in an inspection area for a long time.Thus, it is desired to detect a dangerous article accurately in a shorttime. Therefore, a screening system according to the embodiment detectsthe dangerous article by narrowing down in two stages of primaryscreening and secondary screening.

An outline of the two-stage screening system will be described withreference to FIGS. 1A and 1B. FIG. 1A illustrates an outline of aprimary screening system. FIG. 1B illustrates an outline of a secondaryscreening system. The screening includes a type using an electromagneticwave and a type using an X-ray. Here, an example using anelectromagnetic wave will be described. An electromagnetic wave used inthe embodiment includes a wave having a wavelength in a range of 1 mm to30 mm. The electromagnetic wave having a wavelength of 1 mm to 10 mm isreferred to as a millimeter wave. The electromagnetic wave having awavelength of 10 mm to 100 mm is referred to as a microwave. When anelectromagnetic wave is irradiated to a target person to be inspected,the electromagnetic wave is reflected by an object on a path on whichthe electromagnetic wave propagates. By measuring the reflectionintensity of electromagnetic wave reflected at a certain distance, it ispossible to determine whether an object present at the distance is abody or a dangerous article such as a handgun or an explosive.

As shown in FIG. 1A, in the primary screening, a wide area in which manypeople gather, such as concourses and entrances of airports, stations,shopping malls, concert halls, and exhibition halls is used as aninspection area. A radar 12 and a camera 14 are installed on theceiling, the wall, or the floor of the inspection area. The camera 14captures an image of a person arranged in the inspection area. A personis recognized from the image of the inspection area captured by thecamera 14. The radar 12 irradiates an electromagnetic wave to therecognized person. The radar 12 repeats to irradiate an electromagneticwave while changing an irradiation direction. The radar 12 performsscanning of a target person with an electromagnetic wave by irradiatingthe electromagnetic wave to a plurality of (at least two) points of thetarget person. An electromagnetic wave irradiation point on the targetperson may be changed electronically or mechanically. In the lattercase, the radar 12 is installed on the ceiling, the wall, or the floorvia a scanning mechanism. The scanning mechanism may change the positionof the radar 12 in a straight line (also referred to as linear scanning)or change the direction of the radar 12 (also referred to as sectorscanning). When a plurality of persons are recognized, the radar 12sequentially irradiates an electromagnetic wave to a plurality ofpersons.

An image capturing area of the camera 14 corresponds to the inspectionarea such that images of all persons in the inspection area can becaptured. It is not necessarily required to capture images of all thepersons in the inspection area at once. The camera 14 may be installedon the ceiling via a movable mechanism, and may capture images of allpersons in the inspection area several times while changing the imagecapturing area. It is understood whether a person presents in theinspection area, based on the image of the camera 14. Thus, the primaryscreening may be started when a person enters into the inspection area.

The purpose of primary screening is to set many people in a wide area astarget persons and to determine the degree of danger relating to thepossibility that the target person possesses a dangerous article.Therefore, in primary screening, it is not necessary to determinewhether the target person possesses a dangerous article, accurately withtaking time. It may be possible to detect a suspicious person who maypossess a dangerous article. Highly accurate detection is not requiredfor primary screening. Highly accurate detection is required forsecondary screening. For example, in primary screening, the reflectionintensity of the target person is automatically determined by theapparatus, and a suspicious person who may possess a dangerous articleis detected. For this reason, an inexpensive in-vehicle millimeter waveradar can be used as the radar 12.

The accuracy of the inspection is proportional to the number ofelectromagnetic wave irradiation points per target person. In primaryscreening, the electromagnetic wave irradiation points per target personis set to several to several tens, and so-called rough scanning isperformed. Thus, the time required for the primary screening for manytarget persons is short.

As shown in FIG. 1B, an inspection location for secondary screening isdifferent from an inspection location for primary screening in manycases. In secondary screening, an area such as ticket gates of stations,check-in counters of airports, baggage inspection areas of airports,escalators and stairs of airports, stations, shopping malls, concerthalls, and exhibition halls, which is narrower than the inspection areain primary screening, is set as an inspection area in many cases.

The primary screening system transmits information regarding thesuspicious person to the secondary screening system. An operation ofsecondary screening (irradiation from the radar 16) may be started whenthe information regarding the suspicious person is received and it isdetected that the suspicious person has entered into the image capturingarea of the camera 18. Therefore, the inspection area for the primaryscreening and the inspection area for the secondary screening may bearranged such that a person who leaves the primary screening area entersthe secondary screening area after the person leaves the primaryscreening area. However, the embodiment is not limited thereto. Asecurity guard may look at the detection results of the primaryscreening system to call and stop a suspicious person and to take thesuspicious person to a secondary screening room. In this case, theinspection area of the secondary screening may be randomly set.Furthermore, in an environment in which people do not move, such as inelevators and seats of concert halls, the inspection location for theprimary screening may be the same as that for the secondary screening.In this case, the inspection area for secondary screening may be thesame as or narrower than the inspection area for primary screening.

The radar 16 and the camera 18 are installed on the ceiling, the wall,or the floor of the inspection area for the secondary screening. Thecamera 18 is equivalent to the camera 14 of the primary screeningsystem, and captures an image of a person in the inspection area.Instead of the single radar 16, a plurality of radars 16 may be providedfor each smaller area in the inspection area.

The radar 16 can perform detection with higher accuracy than that of theradar 12 of the primary screening system. That is, the radar 16 does notdetermine the degree of danger relating to the possibility that thetarget person possesses a dangerous article, but specifically determineswhat the target person possesses. In the secondary screening system, forexample, the interval between the irradiation points of the radar 16 isshorter than the interval between the irradiation points of the radar12. Alternatively, the number of irradiation points of the radar 16 isgreater than the number of irradiation points of the radar 12. Ascanning direction of the radar 16 is not one-dimensional buttwo-dimensional, in many cases. The radar 16 may perform high-definitionimaging based on the distribution of electromagnetic wave reflectionintensity. If imaging is performed in the secondary screening, and whatthe target person possesses is displayed as an image, it can bedetermined whether a possessed object is a dangerous article by anoperator viewing the image or by analyzing the image. In the primaryscreening, if the size is equal, a smartphone, a tablet terminal, andthe like may be erroneously detected as a handgun. However, in thesecondary screening, a smartphone and a tablet terminal can bedistinguished from a handgun. The secondary screening is not limited tobeing performed by the apparatus shown in FIG. 1B, and may be performedby a body touch by a security guard or the like or a security guard witha handy scanner.

Since the target person who is inspected in detail in the secondaryscreening is limited to the suspicious person detected in the primaryscreening, the time required for the entirety of two-stage screening isshorter than the time required for inspecting all people in theinspection area for the primary screening in detail.

Configuration of Apparatus for Primary Screening

FIG. 2 is a block diagram illustrating an example of an electricalconfiguration of the primary screening system. The primary screeningsystem includes the radar 12 and the camera 14 schematically shown inFIG. 1A. The primary screening system further includes a CPU 22 as acontroller that executes a program for screening to control the entiretyof screening. The camera 14, a scanning device 32, a storage device 34,a main memory 36, a display device 38, a keyboard 40, and acommunication device 42 are connected to a system bus 24 of the CPU 22.Although not shown in FIG. 1A, the scanning device 32 is installed onthe ceiling, the wall, or the floor of the inspection area. In the radar12, the irradiation direction or the position of the irradiation pointof electromagnetic wave is changed by the scanning device 32. Thus, atarget person or an object held by the target person is scanned with anelectromagnetic wave.

The radar 12 includes a transmit-and-receive antenna 26 and a signalprocessor 28. The signal processor 28 is connected to the system bus 24of the CPU 22. The transmit-and-receive antenna 26 includes one or moretransmit antennas and one or more receive antennas. In a case where aplurality of transmit antennas and a plurality of receive antennas areprovided, the irradiation direction or the position of the irradiationpoint of electromagnetic wave can be electronically changed by anelectronic scanning circuit (not shown) provided in the signal processor28. The mechanical scanning device 32 can be omitted. Further, both themechanical scanning device 32 and the electronic scanning circuit may beprovided. In a case where the camera 14 is installed via a movablemechanism, the movable mechanism is also connected to the system bus 24of the CPU 22.

The storage device 34 is a non-volatile storage device that storesprograms executed by the CPU 22 and various data, and includes an HDD,an SSD, and the like. The main memory 36 is a volatile memory thatstores programs and data read from the storage device 34 or storesvarious data generated during screening. The CPU 22 executes the programthat has been read from the storage device 34 and developed in the mainmemory 36.

The keyboard 40 and the display device 38 are provided as necessary. Thekeyboard 40 may be provided to input setting information of detectionaccuracy, adjustment instructions, and the like. The display device 38may display information such as an image of the detected suspiciousperson. The communication device 42 transmits the result of the primaryscreening to the secondary screening system. The result of the primaryscreening is information for identifying the suspicious person, forexample, an image of the person, a characteristic parameter, and adetection time. In a case where the degree of danger is output in a formof multiple values (quite dangerous, moderately dangerous, moderatelysafe, quite safe, and the like) instead of binary (dangerous or safe) inthe primary screening, the communication device 42 may also transmit thedegree of danger to the secondary screening system. The secondaryscreening system may change the detection accuracy or the screeningmethod in accordance with the degree of danger.

Elements in FIG. 2 other than the radar 12, the camera 14, and thescanning device 32 may be realized as a single device for eachinspection area, or may be arranged on a network, and be commonlyconnected to radars 12, cameras 14, and scanning devices 32 in aplurality of inspection areas through the network. The elements in FIG.2 other than the radar 12, the camera 14, and the scanning device 32 maybe implemented as a PC on a desk in a monitoring room. The signalprocessor 28 may be configured separately from the transmit-and-receiveantenna 26. Only the transmit-and-receive antenna 26 may be installed onthe ceiling, the wall, or the floor of the inspection area, and thesignal processor 28 may be included in the PC.

FIG. 3 is a block diagram illustrating an example of an electricalconfiguration of the radar 12. The transmit-and-receive antenna 26includes at least one transmit antenna 26A and at least one receiveantenna 26B. The transmit antenna 26A and the receive antenna 26B maynot be provided separately, but may perform transmission and receptionin one antenna. A signal generated by a synthesizer 52 is amplified by apower amplifier 54. Then, the amplified signal is supplied to thetransmit antenna 26A, and thus an electromagnetic wave is irradiatedfrom the transmit antenna 26A to the inspection area. The irradiatedelectromagnetic wave is reflected by all objects in the inspection area,and the reflected wave is received by the receive antenna 26B. Areceived signal output from the receive antenna 26B is input to a firstinput terminal of a mixer 58 through a low noise amplifier 56. An outputsignal of the synthesizer 52 is input to a second input terminal of themixer 58.

The mixer 58 mixes the transmit signal from the synthesizer 52 and thereceived signal from the antenna 28B to generate an intermediatefrequency signal. The intermediate frequency signal is input to an A/Dconverter (ADC) 62 through a low-pass filter (LPF) 60. A digital signaloutput from the A/D converter 62 is analyzed by a fast Fouriertransformation (FFT) circuit 64, and the reflection intensity ofelectromagnetic wave of the object is obtained as will be describedlater.

Detection Principle of Primary Screening

As described above, in the primary screening, rough scanning isperformed with a small number of irradiation points. A scanning range ofthe primary screening is narrowed down to some of all target persons notto all the target persons in order to determine an object reflecting theelectromagnetic wave even with a small number of irradiation points. Forthis narrowing down, as shown in FIG. 1A, the camera 14 captures imagesof people in the entirety of the inspection area. An area in which aperson presents is extracted from the captured image of the camera 14,and as shown in FIG. 4A, a plurality of persons are targeted one by one.Furthermore, an inspection part in which a dangerous article is likelyto be hidden is extracted from the image of the target person. As anexample of an inspection part, a body is extracted. Since a dangerousarticle may be hidden not by the target person, but in an object held bythe target person, the object held by the target person may be set asthe inspection part. As an example of the object held by the targetperson, a large bag, suitcase, a case, a rucksack, and a paper bag areselected. The extraction of the person in the image may be performed byany method as long as the person included in the image can be extractedfrom image information. For example, the extraction of the person isperformed by a method including pattern recognition and the like basedon movement in the image or a method using AI, machine learning or thelike. Extraction of the inspection part of the target person isperformed by a method using machine learning.

For easy descriptions, it is assumed that a dangerous article 72 such asa handgun is hidden between the skin of the abdomen and the clothes, andthe body is the inspection part.

Further, since the dangerous article have a certain size, the dangerousarticle can be detected only by scanning one-dimensionally withoutscanning the inspection part two-dimensionally. For this reason, ascanning line for one-dimensionally scanning the inspection part isspecified. For example, a scanning line in a vertical direction, whichpasses through the center of the body in a width direction is specified.The scanning device 32 is driven such that an electromagnetic wave isirradiated at predetermined intervals along this scanning line, and theirradiation direction of the radar 12 is changed in a sector shape.

During the change of the irradiation direction of the radar 12 by thescanning device 32, an electromagnetic wave is irradiated once or aplurality of times every time the irradiation direction coincides withpredetermined irradiation directions. When the electromagnetic wave isirradiated in these directions, irradiation points are arranged atpredetermined intervals on the scanning line of the inspection part.Thus, as shown in FIG. 4B, an electromagnetic wave is irradiated toseveral points at predetermined intervals along the scanning line of thebody of the target person. The electromagnetic wave is reflected by allobjects on the irradiation path of electromagnetic wave. The receivedsignal output from the receive antenna 26B indicates the reflectionintensity of all objects on the irradiation path. Therefore, it isnecessary to extract a received signal component by the reflection wavereflected by the target person from a received signal by multiplereflection waves. The reflection wave is received at a time delayed froman irradiation time by a time corresponding to the distance to theobject. Therefore, if the distance to the target person is known, it ispossible to extract the received signal component by the reflection wavereflected by the target person from the received signal based on areception timing. In a case where one camera is used, the distance tothe target person can be calculated from images with different times andfocuses and the like. The distance can also be calculated by using aplurality of cameras.

If the received signal of the reflection wave from the target person isextracted, the reflection intensity of electromagnetic wave is detectedfrom the amplitude, and thus it is possible to detect a person who issuspected of possessing the dangerous article 72.

The detection principle of the radar 12 will be described. Variouscombinations of transmit-and-receive antennas of the radar 12 areprovided. For example, a plurality of receive antennas receive areflection wave of an electromagnetic wave irradiated from one transmitantenna, one receive antenna receives reflection waves ofelectromagnetic wave irradiated from a plurality of transmit antennas,or a plurality of receive antennas receive the reflection wave of anelectromagnetic wave irradiated from a plurality of transmit antennas.Here, a method of obtaining reflection intensity in a case where onereceive antenna receives the reflection wave of electromagnetic waveirradiated from one transmit antenna will be described.

The synthesizer 52 generates a frequency modulated continuous wave(FMCW) having a frequency which increases linearly with time. The FMCWsignal is also called a chirp signal. The chirp signal is as shown inFIG. 5A when the amplitude A is expressed as a function of time t, andis as shown in FIG. 5B when the frequency f is expressed as a functionof time t. As shown in FIG. 5B, the chirp signal is represented by acenter frequency f_(c), a modulation bandwidth f_(b), and a signal timewidth T_(b). The slope of the chirp signal is called a frequency changerate (chirp rate) γ.

A transmission wave S_(t)(t) of the FMCW signal radiated from thetransmit antenna 26A is represented by Equation 1.

S _(t)(t)=cos[2π(f _(c) t+γt ²/2)]  Equation 1

The chirp rate γ is represented by Equation 2.

γ=f _(b) /T _(b)  Equation 2

At this time, the reflection wave from a target separated by a distanceR from the transmit-and-receive antenna 26 is observed with a delay ofΔt=2R/c from a transmission timing. c indicates the speed of light. Thereceived signal S_(r)r(t) is represented by Equation 3 if the reflectionintensity of the target is set as “a”.

S _(r)(t)=a·cos[2πf _(c)(t−Δt)+πγ(t−Δt)²]  Equation 3

FIG. 6 illustrates the detection principle in a case where a pluralityof objects, for example, three objects are present. FIG. 6(a)illustrates a relation between the transmit signal/received signal andtime. The frequency of the transmit signal changes linearly with time.The received signal is delayed by At with respect to the transmitsignal. In a case where a plurality of objects are provided, thereflection wave from the nearest object is received earliest as shown bya broken line, and the reflection wave from the farthest object isreceived latest as shown by a one-dot chain line.

As shown in FIG. 3, the received signal is mixed with the transmitsignal by mixer 58 and the mixed signal is input to the LPF 60. Theoutput signal of the LPF 60 is referred to as an IF signal z(t) and isrepresented by Equation 4.

z(t)−a·cos(2πΔtγt)  Equation 4

FIG. 6(b) illustrates the relation between the frequency of the IFsignal and time. In an ideal environment with no noise or the like, thefrequency is constant for each reflection wave. The frequency of thereflection wave from the nearest object is the lowest as shown by thebroken line, and the frequency of the reflection wave from the farthestobject is the highest as shown by the one-dot chain line.

The reflection intensity in a frequency domain can be calculated byperforming FFT of the IF signal z(t) in a time domain, which isrepresented by Equation 4, in the FFT circuit 64. Thus, the amplitude ateach point of the FFT result in the frequency domain corresponds to thereflection intensity for each distance from the radar. The frequency andthe distance from the radar have a relation of Equation 5.

f _(if) =Δtγ=2Rγ/c  Equation 5

FIG. 6(c) illustrates the relation between the reflection intensityobtained by performing FFT on the IF signal in the time domain and thefrequency. As described above, it is possible to obtain the reflectionintensity for each distance from the radar by obtaining the amplitude ofthe frequency domain signal of the IF signal.

For example, it is assumed that the distance from the radar 12 to thetarget person is detected as 2 meters from the image informationcaptured by the camera 14. The frequency f_(if) of the IF signalcorresponding to the point at the distance R=2 meters is obtained fromEquation 5. Therefore, it is possible to extract the reflectionintensity at the frequency f_(if) as the reflection intensity of thetarget person, from the reflection intensity of many received signals asshown in FIG. 6(c).

The above-described processing is performed for each irradiation pointin a scanning direction.

Here, as shown in FIGS. 4A and 4B, it is assumed that an electromagneticwave is irradiated toward several points along the scanning line in thevertical direction at the approximate center of the body of the targetperson. As shown in FIG. 4B, the reflection intensity of electromagneticwave of the target person is obtained at several irradiation points.Since the half-value width of electromagnetic wave is about 10 degrees,and the beam width of the radar is sufficiently narrow, the distributionof the reflection intensity of electromagnetic wave on the scanning linevaries depending on the substance that reflects the electromagnetic waveas shown in FIGS. 7A to 7C. FIG. 7A illustrates reflection intensitydistribution of electromagnetic waves in a case where the target personpossesses nothing. In this case, since the electromagnetic wave isreflected by the skin of the target person, the reflection intensity ofelectromagnetic wave does not change regardless of the position of theirradiation point, and the distribution of the reflection intensity isflat distribution. FIG. 7B illustrates the reflection intensitydistribution of electromagnetic wave in a case where the target personpossesses a handgun (metal) in the approximate center of the body. Inthis case, since the reflection intensity of metal is higher than thatof the skin, the reflection intensity of electromagnetic wave at theirradiation point corresponding to the position of the handgun is higherthan the reflection intensity of electromagnetic wave at other points.Since a horizontal axis indicates the reflection intensity (the right isthe higher reflection intensity), the reflection intensity ofelectromagnetic wave has distribution protruding to the right.

FIG. 7C illustrates the reflection intensity distribution ofelectromagnetic wave in a case where the target person possesses anexplosive at the approximate center of the body. Since the explosiveabsorbs an electromagnetic wave more than that by the skin, thereflection intensity at the irradiation point corresponding to theposition of the explosive is lower than the reflection intensity atother points, and the reflection intensity of electromagnetic wave has adistribution protruding to the left. The distribution can be specifiedby a difference between values of reflection intensity in at least twopoints.

According to the embodiment, since it may be possible to determinewhether a person possesses an object, a high resolution corresponding toa difference (for example, 1 cm) between the clothes and the body is notrequired as the resolution in a distance direction. The resolution ofabout several centimeters is enough. Therefore, an in-vehicleinexpensive millimeter-wave radar that is currently distributed in largequantities can be used as the radar 12 in the embodiment.

As described above, if the reflection intensity of the target person iscaptured at several (at least two) points on the scanning line, the CPU22 can determine the degree of danger relating to the possibility thatthe target person possesses the dangerous article, based on a differencein a distribution shape of the reflection intensity of electromagneticwave. The CPU 22 may calculate the degree of danger in a binary manner(dangerous or safe), or may obtain the degree of danger with multiplevalues indicating the degree of danger (for example, quite dangerous,moderately dangerous, moderately safe, quite safe, and the like). Thetype of the degree of danger to be obtained depends on the operation onhow to combine the primary screening and the secondary screening. TheCPU 22 can determine the degree of danger with artificial intelligence.As an example of the artificial intelligence, the CPU 22 can determinethe degree of danger with machine learning. The CPU 22 may determine thedegree of danger using a table. Further, the embodiment is not limitedto the determination by the CPU 22, and the degree of danger may bedetermined by visual observation of the operator. For example, thereflection intensity distribution of electromagnetic wave as shown inFIGS. 7A to 7C may be displayed in the display device 38, and theoperator may visually view the shape thereof and determine the degree ofdanger. Any other method may be used for a determination method of thedegree of danger, and the embodiment is not limited to theabove-described method.

In a case using machine learning, an arithmetic operation circuitrepresenting a model (neural network or the like) for determining thedegree of danger from the reflection intensity of electromagnetic waveat each point is defined. The model includes nodes of multiple stages. Aparameter indicating coupling strength for transmitting informationbetween the nodes is defined. The reflection intensity ofelectromagnetic wave at each point is input to an input stage, and thedegree of danger is output from a node at an output stage. In a case ofsupervised learning, the reflection intensity of electromagnetic wave ateach point is input to the arithmetic operation circuit. The parameteris learned such that the degree of danger output from the arithmeticoperation circuit approaches the degree of danger as teacher data givenby the manufacturer or learning specialist of the screening system.

Various people possessing various kinds of dangerous articles such ashandguns and explosives are made to walk in an area having a possibilityof being set as the inspection area for the primary screening, such asthe concourses and the entrances of airports, stations, shopping malls,concert halls, and exhibition halls or in various locations equivalentto the inspection area in terms of an electromagnetic wave. Thereflection intensity distribution of electromagnetic wave for the peopleis obtained. In this manner, learning of the parameter is performed.

Learning is performed before shipment, and the primary screening systemis shipped in a state where the value of the learned parameter is storedin the storage device 34. During screening after shipment, the CPU 22reads the value of the parameter from the storage device 34 and sets theread value to the value of the parameter in the arithmetic operationcircuit. Thus, if the measured reflection intensity of electromagneticwave is input to the arithmetic operation circuit, the degree of dangeris output from the arithmetic operation circuit.

In a case where the primary screening system is operated by theoperator, learning may also be performed during screening aftershipment. That is, learning may be performed further in a manner thatthe reflection intensity of electromagnetic wave as shown in FIGS. 7A to7C may be displayed in the display device 38, and the degree of dangerdetermined by the operator viewing the reflection intensity may be inputfrom the keyboard 40. Alternatively, even in a case where the result ofthe secondary screening is fed back from the secondary screening systemto the primary screening system, learning may be further performed basedon the degree of danger output by the arithmetic operation circuit andthe secondary screening result.

During machine learning, a synthetic aperture technique or the like maybe applied to the reflection intensity of a plurality of electromagneticwaves, which is obtained at a plurality of reflection points, andlearning may be performed using reflection intensity with the improvedresolution. In addition, as disclosed in U.S. patent application Ser.No. 16/555,381 (Japanese Patent Application No. 2018-214769), thereceived signals may be synthesized using an array antenna includingsparse antenna elements, and thus received signals of antenna elementsmore than the actual antenna elements may be obtained by calculation inorder to enhance the resolution of the received signals. Learning may beperformed using the reflection intensity having an improved resolutionthat is obtained from the calculated received signals.

The above descriptions are provided for a case where one transmitantenna and one receive antenna are provided. Next, a case where aplurality of transmit antennas and a plurality of receive antennas areprovided will be described. In a case where N (>1) transmit antennas andM (>1) receive antennas are provided, the N transmit antennas transmitan electromagnetic wave in a time division manner, and the M receiveantennas continuously performs reception. If the electromagnetic wave isirradiated from N transmitting antennas in the time division manner forN times in total, reception data in N×M channels is obtained. It ispossible to improve the accuracy of determining the degree of danger, byusing the reflection intensity of electromagnetic waves from thereception data in a plurality of channels.

FIG. 8 illustrates the result obtained by performing machine learningwith a human phantom, according to the embodiment. Regarding a case ofonly the human phantom, a case of the human phantom and guns, and a caseof the human phantom and flour (absorption of electromagnetic wave isconsidered as being equivalent to that for an explosives), the distanceto the human phantom is set at various distances, and an electromagneticwave is irradiated at various intervals (scanning intervals). Theirradiation points on the human phantom are arranged in aone-dimensional direction as shown in FIGS. 4A and 4B. FIG. 8illustrates comparison of the accuracy rate when the interval betweenthe irradiation points is 8 mm (43 irradiation points), 16 mm (22irradiation points), 32 mm (11 irradiation points), and 64 mm (6irradiation points) The wavelength of electromagnetic wave is 4 mm. Inthe radar, as the interval between the irradiation points becomes asshort as possible, the accuracy becomes higher, and the interval betweenthe irradiation points is generally set to be a half wavelength ofelectromagnetic wave. The interval of 8 mm is four times the halfwavelength, which is a rough interval. It is understood that theaccuracy rate of 90% or more is obtained even when the interval of theirradiation point is 16 times the half wavelength (32 mm interval), andthe accuracy rate is 70% even when the interval of the irradiation pointis 32 times (64 mm interval). For this reason, it is possible todetermine the degree of danger with accuracy of a certain degree even inthe primary screening based on the distribution of the reflectionintensity of a few irradiation points.

Example of Primary Screening

FIG. 9 is a flowchart illustrating an example of a flow of processing inthe CPU 22 that executes a screening program.

The CPU 22 captures an image signal from the camera 14 in step S102 atpredetermined intervals.

In step S104, the CPU 22 detects all persons appearing in the image.

In step S106, the CPU 22 designates one person as a target person.

In step S108, the CPU 22 extracts a part that is likely to possess adangerous article from the image of the target person, for example, thebody, as an inspection part, and obtains a distance to the inspectionpart. The reason why the part is set to be an inspection target is tonarrow down the irradiation range of electromagnetic wave and to shortenthe inspection time. Therefore, depending on the situation, a belongingsuch as a bag may be extracted as an inspection part. That is, theinspection part may be changed depending on the situation of theinspection area, the target person, and the like. In a case where onecamera is used, the distance from the radar 12 to the inspection part iscalculated from images captured at different times and focuses and thelike. In a case where a plurality of cameras are used, it is possible toobtain the distance based on the parallax of a plurality of images.

In step S112, the CPU 22 drives the scanning device 32 to change thedirection of the radar 12. The irradiation direction of theelectromagnetic wave changes one-dimensionally along a vertical line(scanning line) passing through the approximate center of the inspectionpart in the width direction, as shown in FIG. 4B. Then, the inspectionpart is roughly scanned with an electromagnetic wave. The degree of“rough” means that the interval between the irradiation points is equalto or greater than a half wavelength of electromagnetic wave. Assumingthat the wavelength of electromagnetic wave is 4 mm, the half wavelengthis 2 mm. In the rough scanning, the interval between irradiation pointsis equal to or greater than 4 mm (twice the half wavelength).

In step S114, the CPU 22 extracts the component of the received signalby the reflection wave reflected at the distance of the inspection partfrom the received signals received by the radar 12, and obtains thedistribution of the reflection intensity of electromagnetic wave at theinspection part. Information on the distance of the inspection part isobtained in step S108.

In step S116, the CPU 22 reads the value of the learned parameter fromthe storage device 34, sets the read value to the value of the parameterof the arithmetic operation circuit representing the model for obtainingthe degree of danger from the reflection intensity of electromagneticwave, and inputs the measured reflection intensity to the arithmeticoperation circuit. The CPU 22 determines whether secondary screening isrequired for the target person in accordance with the degree of dangeroutput from the arithmetic operation circuit. In a case where the degreeof danger indicating that the possibility that the target personpossesses a dangerous article is high is obtained, the CPU 22 determinesthat the secondary screening is required.

In a case where it is determined that the secondary screening isrequired, the CPU 22 causes the communication device 42 to notify thesecondary screening system or the person in charge of secondaryscreening of a message indicating that the secondary screening isrequired, in step S118. The content of the notification includesinformation for identifying the target person who is determined torequire secondary screening, for example, an image of a person, acharacteristic parameter, and a detection time. In a case where theprimary screening system detects the degree of danger, the secondaryscreening system may be notified of the degree of danger.

In a case where the CPU 22 determines, in step S116, that the secondaryscreening is not required, or after step S118, the CPU 22 determines, instep S122, whether or not inspection of all the persons has ended.

If the CPU 22 determines that the inspection of all the persons hasended, the process of FIG. 9 ends. If the CPU 22 determines that anunexamined person remains, the CPU 22 designates a target person to beinspected next among the unexamined persons in step S124, and performsthe process of step S108 again.

Thus, according to the embodiment of the primary screening system, it ispossible to determine the degree of danger based on the difference ofthe value of the reflection intensity of electromagnetic wave at severalpoints of the inspection part of the target person. The degree of dangerindicates that the possibility that the target person possesses adangerous article is high. The necessity of secondary screening can bedetermined based on the degree of danger. If it is determined that thesecondary screening is required, the secondary screening system can benotified of information regarding a target person with a certain degreeof danger. Thus, it is possible to inspect only the suspicious person indetail by the secondary screening. Accordingly, the screening systemthat detects the dangerous article by narrowing down in two stages ofprimary screening and secondary screening is realized.

Modification Examples of Primary Screening System

In the flowchart of FIG. 9, the CPU 22 performs step S102 being a startstep of screening, at predetermined intervals. However, the CPU 22 maycontinuously determine whether a person presents in the image capturedby the camera 14. When detecting the person, the CPU 22 may designatethe person as the target person, and then start the process from theprocess of extracting the inspection part from the target person in stepS108.

In step S108, the CPU 22 obtains the range (distance from the radar tothe inspection part) of the reflection wave detected by the radar 12,based on the image captured by the camera 14. However, the embodiment isnot limited thereto, and the range may be obtained based on scanning bythe radar 12. From the result (FIG. 6(c)) obtained by performing FFT onthe received signal obtained by the radar 12 scanning the target person,the distance R at which the reflection intensity of electromagnetic waveis the maximum may be set as the distance from the radar to theinspection part t. Further, the range of the reflection wave may beobtained using another method.

In the above descriptions, the radar 12 is installed on the ceiling, andthe sector scanning is performed. A modification example relating toinstallation of the radar 12 and scanning by the scanning device 32 willbe described below.

FIG. 10A illustrates an example in which the radar 12 irradiates anelectromagnetic wave to the target person in a horizontal direction fromthe side of the target person. A guide rail 32 a extending in thevertical direction may be installed on the floor of the inspection areaor along the wall of the inspection area. A slider 32 b is attached tothe guide rail 32 a to be slidable. The radar 12 is attached to theslider 32 b to irradiate an electromagnetic wave in the horizontaldirection. The scanning device 32 slides the slider 32 b in the verticaldirection along the guide rail 32 a.

Thus, the radar 12 that irradiates an electromagnetic wave in thehorizontal direction moves up and down in the vertical direction, andlinear scanning of the inspection part of the target person isperformed. As a result, similarly to the example of FIGS. 4A and 4B, anelectromagnetic wave can be irradiated to several points along thescanning line in the vertical direction, which passes through theapproximate center of the body of the target person in the widthdirection.

In FIGS. 4A, 4B, and 10A, for easy descriptions, the target person isarranged in front of the radar 12. However, since the target personoften moves, it cannot be guaranteed that the target person is arrangedin front of the radar 12. Even though the target person shifts from thefront of the radar 12, the degree of danger of the target person can bedetermined so long as the electromagnetic wave is irradiated to thedangerous article 72, and the reflection wave from the dangerous article72 is received by the receive antenna.

FIG. 10B illustrates another example in which the radar 12 can performsector scanning in the horizontal plane such that the electromagneticwave is reflected by the dangerous article 72 and the degree of dangercan be determined even if the target person moves. FIG. 10B is a diagramwhen the radar 12 and the slider 32 b are viewed from the top. The radar12 is attached to the slider 32 b to be rotatable in a horizontal planearound an axis al parallel to the guide rail 32 a. The scanning device32 slides the slider 32 b in the vertical direction and rotates theradar 12 in the horizontal plane. Even in a case where the target personmoves, it is possible to irradiate the electromagnetic wave toward thetarget person by rotating the radar 12 in the horizontal plane by thescanning device 32.

FIG. 11 illustrates an example in which the radar 12 is installed on theside of the target person. A two-dimensional array antenna 74 in whichtransmit-and-receive antenna elements 76 equivalent to thetransmit-and-receive antennas 26 of the radar 12 are two-dimensionallyarranged may be installed on the wall of the inspection area. Thetwo-dimensional array antenna 74 may be installed on the floor of theinspection area to be perpendicular to the floor. The two-dimensionalarray antenna 74 is connected to a signal processor (not shown)equivalent to the signal processor 28 shown in FIG. 3.

When the two-dimensional array antenna 74 is used, the electromagneticwave can be transmitted from one of the antenna elements 76, areflection wave can be received by the one of the antenna elements 76.The one of the antenna elements 76 that transmits the electromagneticwave can be sequentially changed. If the transmitting antenna element 76is changed along a the scanning line in the vertical direction whichpasses through the approximate center of the body of the target personin the width direction, the electromagnetic wave can be irradiated toseveral points along the scanning line, similarly to the example ofFIGS. 4A and 4B.

If beam forming is performed using a plurality of antenna elements 76,the irradiation direction of the electromagnetic wave can beelectrically changed to any direction.

Radars corresponding to the radar 12 shown in FIGS. 4A, 10A, and 10B ortwo-dimensional array antennas corresponding to the two-dimensionalarray antenna 74 shown in FIG. 11 may be installed in a plurality ofdirections of the target person. FIG. 12 illustrates an example in whichthe radars 12-1 and 12-2 shown in FIGS. 10A and 10B are installed on thefront and the rear of the target person, as an example. In FIGS. 4A, 4B,10A, 10B, and 11, it is assumed that the target person hides a dangerousarticle on the abdomen. Therefore, the electromagnetic wave isirradiated from the front to the target person. In FIG. 12, it isassumed that the target person hides the dangerous article at locationsother than the abdomen. It is assumed that the target person carries therucksack 78 and hides the dangerous article 72 in the rucksack 78. Inthis case, the electromagnetic wave irradiated from the front of thetarget person is reflected by the chest of the target person and is noteasily irradiated to the dangerous article 72 in the rucksack 78.However, the electromagnetic wave irradiated from the rear of the targetperson is irradiated to the dangerous article 72 in the rucksack 78, andthe reflection wave from the dangerous article 72 is received by theradar 12.

Therefore, a guide rail 32 a-1 is installed on the floor in front (orrear) of the inspection area, and a guide rail 32 a-2 is installed onthe floor on the rear (or front) of the inspection area. The guide rails32 a-1 and 32 a-2 may be installed along the front and the rear walls ofthe inspection area. A slider 32 b-1 is attached to the guide rail 32a-1 and a slider 32 b-2 is attached to the guide rail 32 a-2. The radar12-1 is attached to the slider 32 b-1 to irradiate an electromagneticwave in the horizontal direction from the front of the inspection area.The radar 12-2 is attached to the slider 32 b-2 to irradiate anelectromagnetic wave in the horizontal direction from the rear of theinspection area. The scanning device 32 slides the sliders 32 b-1 and 32b-2 in the vertical direction along the guide rails 32 a-1 and 32 a-2.

Thus, the radars 12-1 and 12-2 that irradiate an electromagnetic wave inthe horizontal direction move up and down in the vertical direction, andlinear scanning of the inspection part of the target person isperformed. As a result, similarly to the example of FIGS. 4A and 4B, anelectromagnetic wave can be irradiated to several points of the body ofthe target person from at least one of the radars 12-1 and 12-2 alongthe scanning line in the vertical direction, which passes through theapproximate center in the width direction. Since it can be determinedfrom the image captured by the camera 14 that the target person iscarrying the rucksack 78, the radar 12-1 or 12-2 that irradiates theelectromagnetic wave may be selected in accordance with the state of thetarget person.

Although not shown, as in FIG. 10B, the radar 12-1 is attached to theslider 32 b-1 to be rotatable in the horizontal plane around an axisparallel to the guide rail 32 a-1. The radar 12-2 is attached to theslider 32 b-2 to be rotatable in the horizontal plane around an axisparallel to the guide rail 32 a-2. Thus, the radars 12-1 and 12-2 arerotated in the horizontal plane by the scanning device 32, and thesector scanning is performed in the horizontal plane.

FIG. 13 illustrates an example in which the radars 12-1 and 12-2 shownin FIGS. 10A and 10B are arranged in the right (or left) and the left(or right) of the target person. It is assumed that the target personcarries a bag 80 in the hand and hides the dangerous article 72 in thebag 80. The intensity of a reflection wave of the electromagnetic waveirradiated from the side by the dangerous article 72 is higher than theintensity of the reflection wave of the electromagnetic wave irradiatedfrom the front (or rear) by the dangerous article 72.

The guide rails 32 a-1 and 32 a-2 are installed on the right and leftfloors of the inspection area. The guide rails 32 a-1 and 32 a-2 may beinstalled along the right and left walls of the inspection area. Sliders32 c-1 and 32 c-2 are attached to the guide rails 32 a-1 and 32 a-2 tobe slidable. The sliders 32 c-1 and 32 c-2 are rotatable about an axisa2 orthogonal to the guide rails 32 a-1 and 32 a-2. The radars 12-1 and12-2 are attached to the sliders 32 c-1 and 32 c-2, respectively, toirradiate an electromagnetic wave to the inspection area in thehorizontal direction. The scanning device 32 slides the sliders 32 b-1and 32 b-2 in the vertical direction along the guide rails 32 a-1 and 32a-2.

Thus, the radars 12-1 and 12-2 that irradiate an electromagnetic wave inthe horizontal direction move up and down in the vertical direction, andlinear scanning is performed. As a result, similarly to the example ofFIG. 12, an electromagnetic wave can be irradiated to several pointsfrom at least one of the radars 12-1 and 12-2 along the scanning line inthe vertical direction, which passes through the center in a front-reardirection of the bag 80 carried by the target person. Since the state,for example, where the target person carries the bag 80 with either handcan be determined from the image captured by the camera 14, the radar12-1 or 12-2 that irradiates an electromagnetic wave may be selected inaccordance with the state of the target person.

Since the sliders 32 c-1 and 32 c-2 are rotatable about the axis a2orthogonal to the guide rails 32 a-1 and 32 a-2, the scanning device 32may not slide the sliders 32 c-1 and 32 c-2 in the vertical direction,but may rotate the sliders 32 c-1 and 32 c-2 around the axis a2. If thesliders 32 c-1 and 32 c-2 are rotated, sector scanning is performed onthe target person in a vertical plane.

Although not shown, similar to FIG. 10B, the radars 12-1 and 12-2 areattached to the sliders 32 c-1 and 32 c-2 to be rotatable in thehorizontal plane around the axis parallel to the guide rails 32 a-1 and32 a-2. Thus, the radars 12-1 and 12-2 are rotated in the horizontalplane, and the sector scanning is performed in the horizontal plane.

If the linear scanning in the vertical direction, the sector scanning inthe vertical plane, and the sector scanning in the horizontal plane arecombined, a possibility that an electromagnetic wave is reflected by thedangerous article increases regardless of the direction of the targetperson.

A sector scanning mechanism in the vertical plane shown in FIG. 13 maybe provided in the slider shown in FIGS. 10A, 10B, and 12.

The examples in FIGS. 10A, 10B, 12, and 13 are examples in which oneradar 12 is attached to one slider 32. A modification example in which aplurality of radars 12 are attached to one slider 32 will be describedwith reference to FIGS. 14A and 14B. FIG. 14A illustrates a modificationexample of FIGS. 10A, 10B, and 12. FIG. 14B illustrates a modificationexample of FIG. 13.

In the example of FIG. 14A, a plurality of, for example, four radars 12a, 12 b, 12 c, and 12 d are attached to a slider 32 d. The slider 32 dhas the same configuration as the slider 32 b shown in FIG. 10A or theslider 32 b-1 or 32 b-2 shown in FIG. 12, but the number of radars 12 tobe mounted is different. The slider 32 d is slidable in the verticaldirection along the guide rail 32. However, in a case where the lengthof the inspection part is small, and four irradiation points are enough,sliding of the slider 32 d in the vertical direction is not required. Ina case where the slider 32 d is slid, the pitch of the slide may be alength corresponding to the height of the slider 32 d having the fourradars 12 a, 12 b 12 c, and 12 d. As described above, if a plurality ofradars 12 are attached to the slider 32 d, an electromagnetic wave canbe irradiated to a plurality of points at a time. Thus, it is possibleto scan the inspection part in a short time. Further, as shown in FIG.10B, the radars 12 a, 12 b, 12 c, and 12 d may be attached to the slider32 d to be rotatable in the horizontal plane around the axis parallel tothe guide rail 32.

In the example of FIG. 14B, a plurality of, for example, four radars 12a, 12 b, 12 c, and 12 d are attached to a slider 32 e. The slider 32 ehas the same configuration as the slider 32 c shown in FIG. 13, and thenumber of mounted radars 12 is different. The slider 32 e is slidable inthe vertical direction along the guide rail 32. However, in a case wherethe length of the inspection part is small, and four irradiation pointsare enough, sliding of the slider 32 e is not required. In a case wherethe slider 32 e is slid, the pitch is a length corresponding to theheight of the slider 32 e having the four radars 12 a, 12 b 12 c, and 12d. Instead of sliding in the vertical direction, the slider 32 e may berotated about the axis a2. Sector scanning is performed on the targetperson in the vertical plane by rotation of the slider 32 e. Asdescribed above, if a plurality of radars 12 are attached to the slider32 e, an electromagnetic wave can be irradiated to a plurality of pointsat a time. Thus, it is possible to scan the inspection part in a shorttime. Further, as shown in FIG. 10B, the radars 12 a, 12 b, 12 c, and 12d may be attached to the slider 32 e to be rotatable in the horizontalplane around the axis parallel to the guide rail 32.

In FIGS. 12 and 13, guide rails 32 a-1 and 32 a-2 are installed in thefront and rear or in the right and left of the inspection area. However,the number of guide rails 32 a installed in the front and rear or in theright and left of the inspection area may be two or more. FIG. 15Aillustrates an example in which two guide rails 32 a are arranged on thefront and rear or on the right and left of the inspection area. The twoguide rails 32 a arranged at the front, rear, left or right of theinspection area may have different linear scanning ranges. For example,the slider 32 b attached to the first guide rail 32 a performs linearscanning in a range from the floor to 1 m above the floor, and theslider 32 b attached to the second guide rail 32 a performs linearscanning in a range from 90 cm above the floor to 2 m above the floor.As the slider 32 b in FIG. 15A, any of the sliders in FIGS. 10A, 10B,12, 13, 14A, and 14B may be used.

FIG. 15B is a plan view illustrating an example in a case where multiplesliders 32 b (guide rails 32 a) are provided evenly around theinspection area. In this example, sliders 32 b (guide rails 32 a) arearranged in eight directions in total, that is, four directions on thefront, rear, left and right of the inspection area, and an obliquedirection intermediate between two adjacent directions in the fourdirections. Thus, regardless of which direction the target person isdirected, any one of the radars 12 can receive the reflection wave fromthe dangerous article. As the slider 32 b in FIG. 15B, any of thesliders in FIGS. 10A, 10B, 12, 13, 14A, and 14B may be used.

As shown in FIGS. 15A and 15B, in a case where a plurality of radars 12are arranged in the inspection area, the radars 12 and the scanningdevices 32 are connected to one CPU 22 and controlled insynchronization. The radars 12 irradiate an electromagnetic wave in atime-division manner and continuously perform reception. Thus, data in aplurality of channels can be received at a time. Since the positions ofthe radars with respect to the target person are different, thereflection intensity at different incident angles with respect to thedangerous article is obtained, and the determination accuracy of thedegree of danger is improved.

As shown in FIGS. 15A and 15B, if a plurality of inspection apparatusesare provided in the inspection area for primary screening, it ispossible to simultaneously inspect a plurality of target persons, and toreduce the inspection time for primary screening more.

In FIGS. 10A, 10B, and 12 to 15B, the guide rail 32 is arranged toextend in the vertical direction. However, the direction of the guiderail 32 extending is not limited to the vertical direction, and may bethe horizontal direction or an oblique direction.

FIGS. 16A to 16G illustrate other modification examples of the scanningline according to the embodiment. FIGS. 16A to 16G are views when thetarget person is viewed from the front.

FIG. 16A illustrates an example in which the body is linearly scannedalong one oblique scanning line. The oblique scanning lines may be ascanning line connecting the lower right and upper left of the body or ascanning line connecting the lower left and upper right of the body. Thescanning direction may be from the bottom to the top or from the top tothe bottom.

FIG. 16B illustrates an example in which the body is linearly scannedalong two intersecting oblique scanning lines. The oblique scanninglines may be a scanning line connecting the lower right and upper leftof the body and a scanning line connecting the lower left and upperright of the body. The scanning direction may be from the bottom to thetop or from the top to the bottom.

FIG. 16C illustrates an example in which linear scanning is performed onthe body along two scanning lines in the vertical direction. Thescanning direction may be from the bottom to the top or from the top tothe bottom.

FIG. 16D illustrates an example in which linear scanning is performed onthe body along one scanning line in the horizontal direction. Thescanning direction may be right to left or left to right.

FIG. 16E illustrates an example in which linear scanning is performed onthe body along two scanning lines in the horizontal direction. Thescanning direction may be right to left or left to right.

In order to realize scanning in FIGS. 16A to 16E, the guide rail 32 ashown in FIGS. 10A, 10B, and 12 to 15B may be installed in the samedirection as the direction of the scanning line, and the radar 12 may beslid along the guide rail 32 a or the direction of the radar 12 may berotated. Alternatively, in a case where the two-dimensional arrayantenna 74 shown in FIG. 11 is used, the antenna element 76 used fortransmission and reception may be selected along the scanning line.

FIG. 16F illustrates an example in which an electromagnetic wave isirradiated to a plurality of points selected randomly within the body.In order to realize this, the antenna element 76 used for transmissionand reception may be selected in accordance with the position of theirradiation point, by using the two-dimensional array antenna 74 shownin FIG. 11.

FIG. 16G illustrates an example in which an electromagnetic wave isirradiated to a plurality of points at predetermined intervals in thebody. In order to realize this, the antenna element 76 used fortransmission and reception may be selected in accordance with theposition of the irradiation points, by using the two-dimensional arrayantenna 74 shown in FIG. 11. Alternatively, in a case where the guiderail 32 a shown in FIGS. 10A, 10B, and 12 to 15B is used, a plurality ofguide rails 32 a may be installed in the vertical direction or thehorizontal direction.

Secondary Screening System

FIG. 17 illustrates an example of the configuration of the secondaryscreening system. The secondary screening system includes an arrayantenna 114A disposed to face a target person 126, a detection device112 connected to the array antenna 114A, and a display device 118connected to the detection device 112. The array antenna 114A isincluded in the radar 16 shown in FIG. 1B. However, FIG. 17 illustratesan example in which the array antenna 114A is installed on the sidesurface instead of the ceiling of the inspection area. The array antenna114A is a two-dimensional array antenna including a plurality of antennaelements 116 arranged two-dimensionally on a rectangular (here, squareas an example) substrate. The substrate is arranged in an X-Y plane. Thesize of the substrate is a size that covers the target person 126. Anelectromagnetic wave is irradiated from each of the antenna elements 116in a Z-direction orthogonal to the substrate.

The detection device 112 can obtain an image of the target person 126 ina plane 124. The plane 124 is in a three-dimensional inspection space122 arranged in the transmission direction of the electromagnetic wavefrom the array antenna 114A and is parallel to the array antenna 114A.The position of the plane 124 in which the image is obtained depends onthe time from transmission to reception of electromagnetic wave. It ispossible to obtain a three-dimensional image of the target person 126 bysetting the time from transmission to reception of electromagnetic wavein accordance with the positions of multiple planes 124 in thethree-dimensional space 122, and obtaining the image of the multipleplanes 124 having different positions. If a one-dimensional arrayantenna in which a plurality of antenna elements are arranged on aone-dimensional line (for example, line in an X-direction) is used as anarray antenna, it is not possible to obtain the three-dimensional image.However, it is possible to obtain a two-dimensional image of the objectin the X-Z plane extending in the irradiation direction ofelectromagnetic wave in a case where the one-dimensional array antennais included.

Although details will be described later with reference to FIG. 18, thearray antenna 114A may include a first sub-array antenna and a secondsub-array antenna that are mixed on the substrate and have differentantenna element intervals. Most of the antenna elements 116 arecomponents of the first sub-array antenna or the second sub-arrayantenna, but some antenna elements 116 are components common to thefirst sub-array antenna and the second sub-array antenna.

The antenna element interval of a general array antenna is anapproximately half wavelength (for easy descriptions, this array antennamay be referred to as a half wavelength array antenna below). However,the antenna element interval of the first sub-array antenna is apositive integer multiple of two or more of the approximately halfwavelength. The antenna element interval of the second sub-array antennais a positive integer multiple of two or more of the approximately halfwavelength. The antenna element interval of the first sub-array antennamay be different from the antenna element interval of the secondsub-array antenna or the antenna element interval of the first sub-arrayantenna and the antenna element interval of the second sub-array antennamay be the same. As described above, the array antenna 114A includes thesparse first sub-array antenna and the sparse second sub-array antennain which the antenna element interval is larger than the approximatelyhalf wavelength, and the antenna elements are sparsely arranged. For thesake of convenience, the first sub-array antenna and the secondsub-array antenna may be referred to as coprime array antennas. In thecoprime array antennas, the antenna element interval (correctly, valueobtained by dividing the element interval by the approximately halfwavelength) is coprime.

The detection device 112 includes a transmitter 132 and a receiver 134connected to each antenna element 116. The transmitters 132 or thereceivers 134 may be used to correspond to the number of the antennaelements 116, and the transmitters 132 or the receivers 134 may beconnected to the antenna elements 116, respectively. The transmitters132 or the receivers 134 may be used to correspond to a value smallerthan the number of the antenna elements 116, and the transmitters 132 orthe receivers 134 may be commonly connected to a plurality of antennaelements 116 through a selector.

A transmission and reception method of the array antenna includes themono-static method in which transmission and reception are performed bythe same antenna element and the bi-static method or the multi-staticmethod in which transmission and reception are performed by separateantenna elements. In the bi-static method, an electromagnetic wave istransmitted from one antenna element and is received by another antennaelement. In the multi-static method, an electromagnetic wave istransmitted from one antenna element and received by a plurality ofother antenna elements. Here, assuming that the mono-static method isemployed, each antenna element 116 is a transmit-and-receive antennaelement.

The transmitter 132 and the receiver 134 are controlled by a controller140 including a CPU and the like. The transmitter 132 and the receiver134 are connected to the controller 140 by wire or wireless. Thecontroller 140 controls the transmission frequency and bandwidth of thetransmitter 132, and the transmission timing for each sub-array antennaand each antenna element 116, and controls the reception timing (timefrom transmission to reception) of the receiver 134 for each sub-arrayantenna and each antenna element 116. A received signal of one antennaelement 116 corresponds to an image signal of one pixel for the targetperson 126. The controller 140 sequentially changes (also refers scans)the antenna elements 116 for each sub-array antenna and changes thereception timing. A reflection wave (by the target person 126) of theelectromagnetic wave transmitted from each antenna element 116 isreceived by the antenna element 116 that has transmitted theelectromagnetic wave.

The received signal received by the receiver 134 is supplied to an imagegeneration circuit 136, and thus a first image signal indicating athree-dimensional image of the target person 126 based on the receivedsignal of the first sub-array antenna and a second image signalindicating a three-dimensional image of the target person 126 based onthe received signal of the second sub-array antenna. As an imagereconstruction algorithm of the image generation circuit 136, a timedomain method, a frequency domain method, or any other algorithm can beused.

The first image signal and the second image signal are supplied to theimage processing circuit 138, and the first image signal and the secondimage signal are combined to generate a synthetic image signal. Theimage generation circuit 136 and an image processing circuit 138 arealso controlled by the controller 140. The image generation circuit 136and the image processing circuit 138 are connected to each other by wireor wirelessly. The receiver 134 and the image generation circuit 136 areconnected to each other by wire or wirelessly. The synthetic imagesignal is supplied to the display device 118. A synthetic image isdisplayed in the display device 118. It is possible to detect that thetarget person 126 possesses a dangerous article (for example, gun) 128,by the operator observing the image. The image processing circuit 138and the display device 118 are connected to each other by wire orwireless.

The detection device 112 includes a communication device 141 connectedto the controller 140. The communication device 141 communicates withthe communication device 42 of the primary screening system shown inFIG. 2 to receive information that has been transmitted from thecommunication device 42 and is for identifying the target persondetermined to require the secondary screening and to receive the degreeof danger. The camera 18 shown in FIG. 1B is connected to the controller140.

FIG. 18 illustrates an example of the array antenna 114A. The arrayantenna 114A has a virtual lattice defined at a predetermined interval d(here, approximately half-wavelength λ/2), and antenna elements 116 (inFIG. 18, the antenna elements are indicated by 142, 144, and 146) arearranged at the intersections of the virtual lattices. As describedabove, in the secondary screening system, since the interval between theirradiation points of electromagnetic wave is short and the number ofirradiation points is large, the detection accuracy of the secondaryscreening system is higher than that of the primary screening system. Inthe array antenna 114A of the secondary screening system, antennaelements are not arranged at all lattice intersections as in a case of ahalf wavelength array antenna, and actual antenna elements are notarranged at most lattice intersections (circles indicated by brokenlines in FIG. 18). The antenna elements 116 of the array antenna 114Ainclude first antenna elements 142, second antenna elements 144, andthird antenna elements 146. The antenna elements 142, 144, and 146 aretwo-dimensionally arranged in the X and Y-directions at intervals thatare several times the lattice interval d, with some exceptions. That is,the antenna elements in the array antenna 114A are arranged to besparser than the antenna elements in the half wavelength array antenna,and the array antenna 114A is sparser than the half wavelength arrayantenna. Thus, interference between adjacent antenna elements does notoccur in the array antenna 114A.

The first antenna elements 142 are arranged in the X-direction with aninterval D1=m×d being m times the approximately half wavelength d. Thesecond antenna elements 144 are arranged in the X-direction with aninterval D2=n×d being n times the approximately half wavelength d. m andn indicate positive integers of two or more which are coprime, forexample, m=3 and n=4. Specific numerical values of m and n are notlimited thereto, and any value may be set.

The first antenna elements 142 are arranged in the Y-direction with aninterval D3=p×d being p times the approximately half wavelength d. Thesecond antenna elements 144 are arranged in the Y-direction with aninterval D4=q×d being q times the approximately half wavelength d. p andq indicate positive integers of two or more which are coprime, forexample, p=3 and q=4. Specific numerical values of p and q are notlimited thereto, and any value may be set. For example, m and p may bedifferent from each other, n and q may be different from each other, andthe distance between the antenna elements may be different in theX-direction and the Y-direction.

The third antenna elements 146 are arranged at the four corners of arrayantenna 114A. The first antenna elements 142 and the third antennaelements 146 constitute the first sub-array antenna having an elementinterval D1=3d. The second antenna elements 144 and the third antennaelements 146 constitute the second sub-array antenna having an elementinterval D2=4d. As described above, the first sub-array antenna and thesecond sub-array antenna are array antennas having antenna elementintervals that are coprime. The third antenna elements 146 are includedin the first sub-array antenna and are included in the second sub-arrayantenna.

The resolution of an image generated using the two array antennas havingantenna element intervals which are coprime is independent from theinterval between the antenna elements of the two array antennas, and isdetermined by the aperture (size) of the array and a beam pattern of theantenna elements. The array size can be freely set, and the arrayantenna can completely cover the target by setting the array size to beequal to the cross-sectional area of the target. The beam pattern is setsuch that the transmit antenna element at any position can transmit anelectromagnetic wave to the target, and the receive antenna element atany position can receive the electromagnetic wave reflected from thetarget. Therefore, the resolution of the image by the array antenna 114Acan be equal to the resolution of the image by the half wavelength arrayantenna. The array antenna 114A has 37 antenna elements. In the halfwavelength array antenna, since antenna elements are arranged at alllattice intersections, the number of antenna elements is 169. The numberof antenna elements of the array antenna 114A can be reduced. If thenumber of antenna elements is small, time taken fortransmission/reception is short, the data volume of the received signalis small, and the calculation time is short.

The characteristics of the array antenna in which antenna elements arearranged at intervals wider than the approximately half wavelength willbe described. If the number of antenna elements is N, the antennaelement interval is D, an excitation phase difference between theantenna elements is β, and the direction of the measurement point in theobject is an angle of θ with respect to the array antenna surface, thepropagation phase difference of the electromagnetic wave transmittedfrom the two antenna elements is kD cos θ. k indicates a wave number.

The total phase shift ψ is represented as follows.

ψ=kD cos θ+β  Equation 6

Considering the round trip of transmission and reception, the wavenumber k is represented by 4π/λ. Thus, the normalized radiation patternis represented as follows.

AF=(1/N)(sin(Nψ/2)/sin(ψ/2))  Equation 7

Equation 7 is a general representation of the radiation pattern of thearray antenna. The maximum value of Equation 7 is obtained in a case asfollows.

ψ=kD cos θ+β=±2mn  Equation 8

Here, m=[0, 1, 2, . . . ]. In many cases, it is desirable thatirradiation becomes a maximum in a direction perpendicular to the axisof the array. In order to obtain a first maximum value in the directionof θ=π/2, the following is necessary.

ψ=kD cos θ+β|_(θ=π/2)=β=0  Equation 9

For this reason, in order for the maximum value of the array factor tobecome a maximum in the direction perpendicular to the axis of the arrayantenna, it is necessary that all antenna elements have the sameexcitation phase. However, since D=λ/2 and β=0, the total phase shift ψis represented as follows.

ψ=kD cos θ+β|_(θ=0,π)=±2π  Equation 10

Substituting ψ in Equation 10 into Equation 7, the maximum value of thearray factor is obtained when θ=0 and π. This means that the arrayfactor has a maximum value at three points (θ=0, π/2, and π). The twoadditional maximum values (θ=0 and π) are called grating lobes. Further,if D=2.5λ and β=0, it is understood that the maximum value at θ=0 shiftsto an angle range of 0<θ<π/2, the maximum value at θ=π shifts to anangle range of π/2<θ<π, and thus two additional grating lobes aregenerated. If the antenna element interval D is increased to 5λ, tengrating lobes are generated on both sides of the main lobe.

Therefore, when the antenna element interval D=nλ/2, n=1, 2, 3, . . . ,the total phase shift ψ is represented as follows.

ψ=kD cos θ+β=2πn cos θ  Equation 11

2πn cos θ_(m)=2mπ  Equation 12

If θ_(m) (m=[0, 1, 2, . . . ]) satisfying Equation 12 is provided, θ_(m)is a set of angles at which the array factor is the maximum value. Thatis, θ_(m) (m=[0, 1, 2, . . . ]) is represented as follows.

θ_(m)=cos⁻¹(m/n)  Equation 13

Since m and n of the antenna element interval D1=m×d (m=3) of the firstsub-array antenna and the antenna element interval D2=n×d (n=4) of thesecond sub-array antenna in FIG. 18 are coprime, Equation 13 representsthat the array factor of the two sub-array antennas simultaneouslybecomes the maximum value in the vertical direction (Z-direction) of thearray.

Therefore, the positions of the grating lobes of the two sub-arrayantennas are different. According to transmission and reception by thearray antenna in which antenna elements are arranged at intervals widerthan the approximately half wavelength, a phantom is generated at theposition of the grating lobe. Thus, the position of the phantomgenerated by the transmission and reception by the two coprime sub-arrayantennas is different. Accordingly, it is possible to remove theinfluence of the phantom by performing image processing on two imagesgenerated by transmission and reception by the two coprime sub-arrayantennas.

As described above, in the array antenna 114A including the first andsecond sub-array antennas in which the antenna element intervals arecoprime, the interval between only some of the antenna elements 142 and144 is d (=λ/2). Since the intervals between most of the antennaelements are 3 d and 4 d, interference between adjacent antenna elementsdoes not occur. In addition, since the antenna elements are sparse, thenumber of antenna elements is small, the transmission/reception time isshort, and the data volume of the received signal is small. Thecalculation time is also short.

The number of coprime sub-array antennas forming the array antenna 114Ais not limited to two, and the array antenna 114A may be configured bythree or more coprime sub-array antennas. In the case of the antennaelement interval D1=m×d of the first sub-array antenna and the antennaelement interval D2=n×d of the second sub-array antenna, m and n arepositive integers of two or more that are coprime.

An example of an image of the target person will be described withreference to FIGS. 19A, 19B, 20, and 21. FIG. 19A illustrates an exampleof a first image generated by transmitting and receiving anelectromagnetic wave using the first sub-array antenna. FIG. 19Billustrates an example of a second image generated bytransmitting/receiving an electromagnetic wave using the secondsub-array antenna. FIG. 20 illustrates a profile (solid line) of animage signal S indicating the first image shown in FIG. 19A in an X-axisdirection, and a profile (broken line) of an image signal S indicatingthe second image shown in FIG. 19B in the X-axis direction. As shown inFIGS. 19A and 19B, the first and second images by the first and secondsub-array antennas include the image of the target at the centerportion, and includes phantoms of the object at the peripheral portions.The position of the phantom is difference between the first image andthe second image. Therefore, if the first image and the second image arecombined (synthesized) by selecting the smaller absolute value of thefirst image signal and the second image signal in each pixel, it ispossible to obtain a synthetic image with no influence of the phantom asshown in FIG. 21.

FIG. 22 is a flowchart illustrating an example of the screening in theradar shown in FIG. 18. The secondary screening starts if thecommunication device 141 receives information for identifying the targetperson determined to require the secondary screening and receives thedegree of danger, from the communication device 42 in the primaryscreening system. For example, the controller 140 continuouslydetermines whether the target person requiring secondary screeningappears in the image captured by the camera 18. If the controller 140detects that the target person has entered into the image, that is, hasentered into the inspection area for secondary screening, the controller140 starts the processing of the flowchart shown in FIG. 22.

In step S252, the controller 140 transmits and receives anelectromagnetic wave using the first sub-array antenna including firstantenna elements 142 and third antenna elements 146. The controller 140controls the transmitter 132 and the receiver 134 such that anelectromagnetic wave is sequentially transmitted from the antennaelements 142 and 146, and the antenna elements 142 and 146 sequentiallyreceive an electromagnetic wave. In step S254, the image generationcircuit 136 generates the first image based on the signals received bythe antenna elements 142 and 146.

In step S256, the controller 140 transmits and receives anelectromagnetic wave using the second sub-array antenna including secondantenna elements 144 and third antenna elements 146. The controller 140may sequentially transmit an electromagnetic wave from the antennaelements 144 and 146 and may control the antenna elements 144 and 146 tosequentially receive an electromagnetic wave. The controller 140 maysimultaneously transmit an electromagnetic wave from all the antennaelements 144 and 146 of the second sub-array antenna, and may controlthe antenna elements 144 and 146 to sequentially receive anelectromagnetic wave. In step S258, the image generation circuit 136generates the second image based on the signals received by the antennaelements 144 and 146.

In step S260, the image processing circuit 138 combines the first imageand the second image by selecting the smaller absolute value of thefirst image signal and the second image signal in each pixel, togenerate a synthetic image having no influence of the phantom. In stepS262, the display device 118 displays the synthetic image.

The operator of the radar 16 can visually view the synthetic image ofthe target person and accurately determine whether the target personpossesses a dangerous article such as a handgun.

According to the secondary screening system shown in FIG. 17, the firstand second images are generated using the first and second sub-arrayantennas having antenna element intervals that are coprime, and thefirst and second images are combined to select the minimum values. Thus,it is possible to obtain an image of a target without a phantom. Sincean electromagnetic wave is transmitted and received by the first andsecond sub-array antennas having antenna element intervals that arecoprime, advantages as follows are obtained. That is, interferencebetween adjacent antenna elements does not occur. In addition, since thenumber of the antenna elements is small, the transmission/reception timeis short, the data volume of the received signal is small, and thecalculation time is short. Further, since the two-dimensional arrayantenna 114A is used, a three-dimensional image of the target can beobtained.

The above description relates to screening of determining whether aperson possesses a dangerous article. However, the above screeningsystem is not limited to a person, and can be applied to checking themail items or parcels collected by a mailer or a carrier or the shieldedcontents of cardboard boxes and other items brought into the factory.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A system comprising: a first device with aprimary screening area; a second device with a secondary screening areadifferent from the primary screening area; and a processor circuitry,wherein: the first device comprises a first antenna and a firstcommunication device; the second device comprises a second antenna and asecond communication device; the first antenna is configured toirradiate an electromagnetic wave to a target in the primary screeningarea and receive an electromagnetic wave reflected by the target; thesecond antenna is configured to irradiate an electromagnetic wave to thetarget in the secondary screening area and receive an electromagneticwave reflected by the target; the processor circuitry is configured todetermine a possibility that the target possesses a predeterminedarticle, based on a level of the electromagnetic wave received by thefirst antenna, and determine that screening by the second device isrequired for the target in accordance with the possibility; the firstcommunication device is configured to transmit, to the second device,first information identifying that screening by the second device isrequired for the target; and the processor circuitry is configured tomake the second antenna start irradiation of the electromagnetic wavewhen the second communication device receives the first information. 2.The system of claim 1, further comprising: a first camera configured tocapture an image including the secondary screening area; wherein theprocessor circuitry is configured to determine whether the target beingrequired to be screened by the second device is in an image captured bythe first camera and to make the second antenna start irradiation of theelectromagnetic wave when it is determined that the target is in theimage.
 3. The system of claim 1, further comprising a first cameraconfigured to capture an image including the secondary screening area,and wherein: the processor circuitry is configured to determine whetherthe target being required to be screened by the second device entersinto the secondary screening area in accordance with an image capturedby the first camera and to make the second antenna start irradiation ofthe electromagnetic wave when it is determined that the target entersinto the secondary screening area.
 4. The system of claim 1, wherein:the second antenna comprises a first sub-array antenna and a secondsub-array antenna; a first antenna element interval of the firstsub-array antenna is different from a second antenna element interval ofthe second sub-array antenna; the processor circuitry is configured togenerate a first image signal based on a signal from the first sub-arrayantenna and a second image signal based on a signal from the secondsub-array antenna; and the processor circuitry is configured to combinethe first image signal and the second image signal to generate asynthesized image by selecting a smaller absolute value of the firstimage signal and the second image signal for each pixel of thesynthesized image.
 5. The system of claim 4, wherein: the first antennaelement interval is m×d; the second antenna element interval is n×d; dis an approximately half wavelength; each of m and n is a positiveinteger of at least two; and m and n are coprime.
 6. The system of claim1, wherein: the first antenna is configured to sequentially irradiate(i) a first electromagnetic wave of a wavelength of 1 mm to 30 mm to afirst position, (ii) a second electromagnetic wave of a wavelength of 1mm to 30 mm to a second position different from the first position, and(iii) a third electromagnetic wave of a wavelength of 1 mm to 30 mm to athird position different from the first position and the secondposition; the first position, the second position, and the thirdposition are respective different positions on the target; and theprocessor circuitry is configured to: obtain a first reflectionintensity of the first electromagnetic wave on the first position,obtain a second reflection intensity of the second electromagnetic waveon the second position, obtain a third reflection intensity of the thirdelectromagnetic wave on the third position, and determine thepossibility that the target possesses a predetermined article, based ona difference between the first reflection intensity and the secondreflection intensity and a difference between the second reflectionintensity and the third reflection intensity.
 7. The system of claim 1,wherein the possibility that the target possesses the predeterminedarticle indicates whether or not the target possesses the predeterminedarticle, or a degree to which it is likely that the target possesses thepredetermined article.
 8. The system of claim 6, further comprising: asecond camera configured to capture an image including the primaryscreening area, and wherein; the processor circuitry is configured to:detect the first position, the second position, and the third positionin the image captured by the second camera; and output an instruction tothe first antenna to irradiate the first electromagnetic wave to thefirst position, the second electromagnetic wave to the second position,and the third electromagnetic wave to the third position.
 9. The systemof claim 8, wherein the processor circuitry is configured to detect, anarea of a body of the target.
 10. The system of claim 1, wherein theprocessor circuitry is configured to determine the possibility by usingmachine learning.
 11. The system of claim 6, wherein the first devicefurther comprises a scanning mechanism configured to move the firstantenna along the line, or to rotate the first antenna to change anirradiation direction of the first electromagnetic wave, the secondelectromagnetic wave, and the third electromagnetic wave in a fan shape.12. The system of claim 1, wherein a number of irradiation points of theelectromagnetic wave irradiated by the second antenna is larger than anumber of irradiation points of the electromagnetic wave irradiated bythe first antenna.
 13. The system of claim 1, wherein: a time forirradiating the electromagnetic wave by the first antenna is shorterthan a time for irradiating the electromagnetic wave by the secondantenna.
 14. The system of claim 1, wherein: the first device comprisesa plurality of first antennas; the second device comprises a pluralityof second antennas; and an interval between the plurality of secondantennas is shorter than an interval between the plurality of firstantennas.
 15. The system of claim 1, wherein: the second device isconfigured to obtain an electromagnetic wave reflection intensity, andfurther comprising: a display configured to display an image based onthe electromagnetic wave reflection intensity.
 16. The system of claim1, further comprising a display configured to display informationrelating to a target for whom screening by the second device isrequired.
 17. The system of claim 1, wherein: the first informationcomprises at least one of an image of the target, a characteristicparameter of the target, and a detection time of the target.
 18. Thesystem of claim 1, wherein: the second device is configured to change adetection accuracy or a screening method in accordance with theprobability.
 19. The system of claim 1, wherein: the processor circuitryconfigured to determine a possibility that the target possesses thepredetermined article, based on a level of the electromagnetic wavereceived by the second antenna, and configured to learn a pair of thepossibility based on a level of the electromagnetic wave received by thefirst antenna and the possibility based on a level of theelectromagnetic wave received by the second antenna.
 20. An inspectionmethod in an inspection system, the inspection system comprising a firstdevice with a primary screening area, a second device with a secondaryscreening area different from the primary screening area, and aprocessor circuitry, the first device comprising a first antenna, and afirst communication device, the second device comprising a secondantenna and a second communication device, and the method comprising: bythe first antenna, irradiating an electromagnetic wave to a target inthe primary screening area and receiving an electromagnetic wavereflected by the target; determining, by the processor circuitry, apossibility that the target possesses a predetermined article, based ona level of the electromagnetic wave received by the first antenna, anddetermining that screening by the second device is required for thetarget in accordance with the possibility; transmitting, by the firstcommunication device to the second device, first information identifyingthat screening by the second device is required for the target; and bythe processor circuitry, making the second antenna start irradiation ofan electromagnetic wave to the target in the secondary screening areaand receiving of an electromagnetic wave reflected by the target whenthe second communication device receives the first information.
 21. Themethod of claim 20, wherein the inspection system further comprises afirst camera configured to capture an image including the secondaryscreening area, and the method further comprises: by the processorcircuitry, determining whether the target being required to be screenedby the second device is in an image captured by the first camera, andmaking the second antenna start irradiation of the electromagnetic wavewhen it is determined that the target is in the image.
 22. The method ofclaim 21, wherein the inspection system comprises a first cameraconfigured to capture an image including the secondary screening area,and further comprising: by the processor circuitry, determining whetherthe target being required to be screened by the second device entersinto the secondary screening area in accordance with an image capturedby the first camera and making the second antenna start irradiation ofthe electromagnetic wave when it is determined that the target entersinto the secondary screening area.
 23. The method of claim 20, whereinthe second antenna comprises a first sub-array antenna and a secondsub-array antenna, a first antenna element interval of the firstsub-array antenna is different from a second antenna element interval ofthe second sub-array antenna, and the method further comprises: by theprocessor circuitry, generating a first image signal based on a signalfrom the first sub-array antenna and a second image signal based on asignal from the second sub-array antenna; and by the processorcircuitry, combining the first image signal and the second image signalto generate a synthesized image by selecting a smaller absolute value ofthe first image signal and the second image signal for each pixel of thesynthesized image.
 24. The method of claim 23, wherein: the firstantenna element interval is m×d; the second antenna element interval isn×d; d is an approximately half wavelength; each of m and n is apositive integer of at least two; and m and n are coprime.
 25. Themethod of claim 20, further comprising: by the first antenna,sequentially irradiating (i) a first electromagnetic wave of awavelength of 1 mm to 30 mm to a first position, (ii) a secondelectromagnetic wave of a wavelength of 1 mm to 30 mm to a secondposition different from the first position, and (iii) a thirdelectromagnetic wave of a wavelength of 1 mm to 30 mm to a thirdposition different from the first position and the second position, thefirst position, the second position, and the third position beingrespective different positions on the target; and by the processorcircuitry, obtaining (i) a first reflection intensity of the firstelectromagnetic wave on the first position, (ii) a second reflectionintensity of the second electromagnetic wave on the second position, and(iii) a third reflection intensity of the third electromagnetic wave onthe third position, wherein the determining by the processor circuitrycomprises determining the possibility that the target possesses apredetermined article, based on a difference between the firstreflection intensity and the second reflection intensity and adifference between the second reflection intensity and the thirdreflection intensity.
 26. The method of claim 20, wherein thepossibility that the target possesses the predetermined articleindicates whether or not the target possesses the predetermined article,or a degree to which it is likely that the target possesses thepredetermined article.
 27. The method of claim 25, wherein theinspection system further comprises a second camera configured tocapture an image including the primary screening area, and the methodfurther comprises, by the processor circuitry: detecting the firstposition, the second position, and the third position in the imagecaptured by the second camera; and outputting an instruction to thefirst antenna to irradiate the first electromagnetic wave to the firstposition, the second electromagnetic wave to the second position, andthe third electromagnetic wave to the third position.
 28. The method ofclaim 27, wherein the detecting the first position, the second position,and the third position comprises detecting an area of a body of thetarget.
 29. The method of claim 20, wherein the determining comprisesdetermining the possibility by using machine learning.
 30. The method ofclaim 25, further comprising at least one of: moving the first antennaalong the line; and rotating the first antenna to change an irradiationdirection of the first electromagnetic wave, the second electromagneticwave, and the third electromagnetic wave in a fan shape.
 31. A systemcomprising: a first device; and a second device, wherein: the firstdevice comprises a first antenna, first processor circuitry, and a firstcommunication device; the second device comprises a second antenna,second processor circuitry, and a second communication device; the firstantenna is configured to irradiate an electromagnetic wave to a targetand receive an electromagnetic wave reflected by the target; the secondantenna is configured to irradiate an electromagnetic wave to the targetand receive an electromagnetic wave reflected by the target; the firstprocessor circuitry is configured to determine a possibility that thetarget possesses a predetermined article with machine learning, based ona level of the electromagnetic wave received by the first antenna; thefirst communication device is configured to transmit, to the seconddevice, first information indicating that further inspection of thetarget is required based on the possibility; the second processorcircuitry is configured to make the second antenna start irradiation ofthe electromagnetic wave when the second communication device receivesthe first information; the second processor circuitry is configured todetermine a possibility that the target possesses a predeterminedarticle, based on a level of the electromagnetic wave received by thesecond antenna; and the machine learning is performed based on thepossibility determined by the first processor circuitry and thepossibility determined by the second processor circuitry.
 32. The systemof claim 31, wherein a number of irradiation points of theelectromagnetic wave irradiated by the second antenna is larger than anumber of irradiation points of the electromagnetic wave irradiated bythe first antenna.
 33. An inspection method in an inspection system, theinspection system comprising a first device and a second device, thefirst device comprising a first antenna, first processor circuitry, anda first communication device, the second device comprising a secondantenna, second processor circuitry, and a second communication device,and the method comprising: by the first antenna, irradiating anelectromagnetic wave to a target and receiving an electromagnetic wavereflected by the target; determining, by the first processor circuitry,a possibility that the target possesses a predetermined article, basedon a level of the electromagnetic wave received by the first antenna;transmitting, by the first communication device to the second device,first information indicating that further inspection of the target isrequired, based on the possibility; by the second processor circuitry,making the second antenna start irradiation of an electromagnetic waveto the target and receiving of an electromagnetic wave reflected by thetarget when the second communication device receives the firstinformation; by the second processor circuitry, determining apossibility that the target possesses a predetermined article, based ona level of the electromagnetic wave received by the second antenna; andmaking the second antenna start irradiation of an electromagnetic waveto the target and receiving of an electromagnetic wave reflected by thetarget when the second communication device receives the firstinformation, wherein: the machine learning is performed based on thepossibility determined by the first processor circuitry and thepossibility determined by the second processor circuitry.
 34. The methodof claim 33, wherein a number of irradiation points of theelectromagnetic wave irradiated by the second antenna is larger than anumber of irradiation points of the electromagnetic wave irradiated bythe first antenna.